1. Field of the Invention
The present invention relates generally to a magnetic sensing element for use in a magnetic sensor or a hard disk and, more particularly, the present invention relates to a magnetic sensing element having an improved sensitivity to magnetic fields, and to a manufacturing method thereof.
2. Description of the Related Art
FIG. 12 is a cross-sectional view showing the structure of a conventional magnetic sensing element manufactured by a conventional manufacturing method as viewed from the face opposing a magnetic medium. The magnetic sensing element shown in FIG. 12 is a spin-valve, which is a type of giant magnetoresistive (GMR) element utilizing the giant magnetoresistive effect. The element detects a magnetic field recorded in a recording medium, such as a hard disk. The spin-valve magnetic sensing element includes a laminate 9, a pair of longitudinal bias layers 6 formed on the laminate 9, and a pair of electrode layers 7 formed on the bias layers 6. The laminate 9 is composed of a substrate 8, an antiferromagnetic layer 1, a pinned magnetic layer 2, a nonmagnetic layer 3, and a free magnetic layer 4.
Generally, the antiferromagnetic layer 1 and the longitudinal bias layers 6 are composed of an Fe—Mn alloy or a Ni—Mn alloy. The pinned magnetic layer 2 and the free magnetic layer 4 are composed of a Ni—Fe alloy, the nonmagnetic layer 3 is composed of Cu, and the electrode layers 7 are composed of Cr.
Referring to FIG. 12, the pinned magnetic layer 2 is preferably put into a single-magnetic-domain state in the Y direction in the drawing (the direction of a leakage magnetic field from the recording medium, i.e., the height direction) by an exchange anisotropic magnetic field generated with the antiferromagnetic layer 1. The magnetization of the free magnetic layer 4 is preferably oriented in the X direction by an exchange anisotropic magnetic field from the longitudinal bias layers 6. In other words, the magnetization direction of the pinned magnetic layer 2 is preferably orthogonal to the magnetization direction of the free magnetic layer 4.
In this spin-valve magnetic sensing element, a sense current is supplied to the free magnetic layer 4, the nonmagnetic layer 3, and the pinned magnetic layer 2 through the electrode layers 7 formed on the longitudinal bias layers 6. A recording medium such as a hard disk moves in the Z direction in the drawing. A leakage magnetic field from the recording medium provided in the Y direction changes the magnetization direction of the free magnetic layer 4 from the X direction toward the Y direction. This change in the magnetization direction of the free magnetic layer 4 with respect to the pinned magnetization direction of the pinned magnetic layer 2 changes the electrical resistance (magnetoresistive effect). The voltage then changes based on the change in the electrical resistance. The leakage magnetic field from the recording medium is thus detected as the change in the voltage.
In a conventional manufacturing method for the spin-valve magnetic sensing element shown in FIG. 12, the antiferromagnetic layer 1, the pinned magnetic layer 2, the nonmagnetic layer 3, and the free magnetic layer 4 are deposited on the substrate 8 in that order to form the laminate 9. Subsequently, the longitudinal bias layers 6 and the electrode layers 7 are formed on the laminate 9.
After deposition, these layers are annealed in a first magnetic field to orient the magnetization of the pinned magnetic layer 2 in the Y direction and then in a second magnetic field to orient the magnetization of the free magnetic layer 4 in the X direction. However, during annealing in the second magnetic field, an exchange anisotropic magnetic field acting at the interface between the antiferromagnetic layer 1 and the pinned magnetic layer 2 is shifted from the Y direction toward the X direction. Accordingly, the magnetization direction of the pinned magnetic layer 2 is no longer orthogonal to the magnetization direction of the free magnetic layer 4. Thus, asymmetry which is the degree of asymmetry in an out waveform, is high. The problem of high asymmetry is especially significant when the antiferromagnetic layer 1 and the longitudinal bias layer 6 are made from the same antiferromagnetic material.
In making the spin-valve magnetic sensing element shown in FIG. 12, a resist layer R for lift-off resist is formed on the laminate 9 subsequent to the formation of the laminate 9, as shown in FIG. 13. The longitudinal bias layers 6 and the electrode layers 7 are then deposited by an ion beam sputtering process. Layers 6a having the same composition as that of the longitudinal bias layers 6 and layers 7a having the same composition as that of the electrode layers 7 are formed on the resist layer R.
During the sputtering process, few sputtered particles are deposited on the region covered by two end portions of the resist layer R. Thus, the longitudinal bias layers 6 and the electrode layers 7 are thin in the region covered by the two end portions of the resist layer R. As shown in FIGS. 12 and 13, the thickness of the longitudinal bias layers 6 and the electrode layers 7 is decreased at two side portions S of the track.
The tapering of the layers 6 and 7 causes the exchange coupling between the free magnetic layer 4 and the longitudinal bias layers 6 to decrease at the two side portions S of the track. Thus, the magnetization direction of the free magnetic layer 4 is not satisfactorily pinned at the two side portions S of the track, such that the magnetization in regions S changes in response to the external magnetic field. Accordingly, when a track in the magnetic recording medium is made narrower to improve the recording density of the magnetic recording medium, not only information on the track, which the region corresponding to the track width Tw intends to read, but also the information on the adjacent tracks may be read by the two side portions S of the track (side reading).